Upload & Sell: Off
YN560-III SPEED LIGHT - $ 86 ($82 each for 5 or more) and apparently works with the existing Yongnuo transmitters. Not sure how many groups or total flash units possbile. $ 80.84 each if you use the Lighting Rumors code by Jan. 31st.
Built in radio, manual power.
If you can do without TTL, Ext. A, and Ext. M, you can buy 7 YN560-III units instead of one 600 EX - RT.